[0001] The present invention relates to a method of purificating titanium tetrachloride
(TiCl
4) and, in particular, to a method of obtaining such chloride which can yield a low
oxygen titanium metal when reduced with magnesium or sodium in the subsequent process.
[0002] Titanium metal is produced on a commercial scale, widely by a process in which titanium
tetrachloride is reduced with magnesium or sodium. As this process is not effective
to remove oxygen impurity, in order to produce a low oxygen metal, it is essential
that the chloride itself should contain a very limited amount of impurity such as
oxides or other oxygen compounds.
[0003] Titanium tetrachloride is generally produced by chlorinating a rutile, whether natural
or synthesized from ilumenite by removing the iron component, in the presence of a
reductive medium such as coke and, subsequently, separating from the primary product
of titanium tetrachloride impurities which are much more volatile or condensable such
as SiCl
4, SnCl
4, AlCl
3, FeCl
3, COCl
2 and Cl
2 in a fractional distillation. Exhibiting a boiling point too close to that of TiCl
4, VOCl
3 as impurity cannot be effectively removed in this process, so the raw chloride is
treated in advance with hydrogen sulfide or pulverized copper, thus converting to
VOC1
- or VOC1 which is much more condensable than titanium tetrachloride. As these treatments
are not very effective for elimination of oxychloride impurities such as TiOCl
2, thus purified TiCl
4 usually exhibits rather a high oxygen level of the order of 0.05 to 0.10% by weight
when finally converted to titanium sponge.
[0004] A more purified chloride, less contaminated with such oxychlorides, has been desirable
for producing a higher quality titanium metal of a lower oxygen level, or for achieving
a higher yield of marketable product.
[0005] Therefore one of the principal objects of the invention is to provide a method of
producing a more oxygen-free titanium tetrachloride which is essential to achieving
such commercial advantages.
[0006] According to the invention there is provided a method for purificating the tetrachloride,
comprising: heating a loose mass of catalytic metal to a temperature over 300°C approximately,
introducing vapor of a crude titanium tetrachloride to contact with said metal, said
chloride comprising a minor amount of metal oxychloride, causing a reaction to convert
a substantial part of the oxychloride to substances which are less volatile than titanium
tetrachloride, removing such substances in condensed state from the titanium tetrachloride
in fluid state, and recovering thus purified titanium tetrachloride.
[0007] While the method of the invention primarily contemplates the removal of other oxychlorides,
it also is effective to decompose the VOC1
3 impurity to more readily disposable subcompounds VOCl
2 and VOC1, so it is not essential any more that the raw chloride be treated with -copper
or hydrogen sulfide when the former is to be treated by the method of the invention.
[0008] Availability as starting material of a VOC1
3 containing raw chloride in this method permits not only to save such pre-treatment
with copper or hydrogen sulfide, but also to provide a possible index to the level
of VOCl
3 and other oxygen compounds in the raw chloride during the process of the invention:
the titanium tetrachloride develops a yellow-brownish color when contaminated with
such impurities and, by the time the chloride looses the color characteristic to VOC1
3, the former also becomes free of other contaminants.
[0009] The crude vapor to be treated by this invention may be supplied immediately, without
effecting any pretreatment to the vapor, from a fractional distillation process. That
allows the overall process plant to take a compact design, although the catalytic
metal may have to be replaced or re-generated more frequently.
[0010] The catalytic metal of the invention may be selected from copper, iron and copper-
and iron based alloys, which are favorable for their high performance considering
the availability and economical advantages.
[0011] A higher catalyst temperature allows a more efficient decomposition of the oxychlorides,
but unfavorably it also results in a higher proportion of TiClZ and TiCl
3 in the yield due to a TiCl
4 decomposition which takes place increasingly as the temperature rises. On the balance
betweeen the efficiency and yield of the process the temperature range of 400 to 650
*C is found optimal with a catalyst of copper, although it promotes the decomposition
of oxychlorides appreciably at temperatures around 300°C, while the range of 600 to
800°C approximately is optimal with iron, although it promotes the process appreciably
about 550°C.
[0012] Among possible iron catalysts carbon steel is found most effective with lowest temperatures
required for the process, and a higher content of chromium or nickel causes to rise
the temperature requirement. In this context, a reaction vessel for the process advantageously
should consist of either chromium- or nickel lined steel or stainless steel containing
such ingredients, so as to effectively suppress the reaction to proceed on the wall.
[0013] The catalyst metal, when consumed by the process in which it is oxidized, can be
treated with a stream of hydrogen gas, for example, for re-generation and, finally,
replaced entirely with a fresh one.
[0014] Oxychlorides for the most part can be converted to less volatile substances and deposit
on or around the catalyst metal in liquid or solid phase, which should be removed
continuously or at intervals.
[0015] The yielding gas is condensed to liquid and then filtered, settled or distilled in
order to remove a minor amont of subchlorides TiCl
2 and TiCl
3, as well as other decomposition products and particulate substances carried in the
yield. A titanium tetrachloride thus purified exhibits normally an oxygen level well
of the order of 0.03 to 0.01%, for example, with much improvement over the level at
0.05% or more with a corresponding crude by a conventional technique.
[0016] Such titanium tetrachloride may be introduced to a reaction vessel loaded of fused
magnesium in inert gas atmosphere. The titanium metal thus deposited is heated to
elevated temperatures under decreased pressures so as to allow the metal and chloride
of magnesium to flow or fly away from the solid product of titanium metal. The latter
as thus recovered shows an oxygen content of 0.01% and a hardness around 60 BHN
1500Kg, an improved quality by far over one of the best quality with the oxygen level at
0.05% and the hardness at 80 BHN
1500Kg which the Applicant could achieve with conventionally produced titanium tetrachloride.
[0017] Now the invention will be described more in detail by means of examples in reference
to the attached drawing. The examples and drawing given herein are for the purpose
of illustration only, and should not be taken as limiting the invention.
[0018] The sole figure shows in section an arrangement for practising the method of the
invention. A closed vertical cylindrical vessel of steel 1 is packed with a mass of
divided catalyst metal 2, which may be in the form of powder, turnings, or other loose
collection which gives a substantially increased surface relative to the volume. The
vessel 1 may be vertical cylindrical for the manufacturability and from the view point
of convenience and physical properties. It is cut around to open on the wall and welded
together to close. Tubes 3 and 4 are connected to the vessel at the bottom and top,
respectively, for feeding crude chloride and exhausting purified chloride. The vessel
as a whole is contained in a vertical cylindrical electric furnace which consists
of two separable portions and dividable along the axis when it is opened for taking
out the vessel.
Example 1
[0019] A cylindrical vessel as schematically shown in the figure was used, which had a 1
m I.D. and a 3 m length, and which consisted of a chromium nickel stainless steel
equivalent to AISI Type 316. The vessel was loaded of 600 Kg of copper foils, heated
to temperatures between 500-550°C, as measured on the vessel wall. Maintaining the
temperature condition, vapor of an oxychloride- contaminated titanium tetrachloride
was passed through the vessel at a rate of 10 Kg/min. The yielding gas was cooled
and condensed to liquid, and settled. A top liquid was filtered to remove solid particles
in suspension. The purified TiCl
4 exhibited an oxygen level of 250 ppm by weight relative to the metal titanium.
Example 2
[0020] The reaction vessel was loaded with 500 Kg of turnings of carbon steel and heated
to temperatures between 600-630°C. The crude chloride was fed at 10 Kg/min. The yielding
gas was removed of solid particles in suspension. The titanium tetrachloride exhibited
an oxygen level of 120 ppm.
1. A method of purificating titanium tetrachloride, comprising: heating a loose mass
of catalytic metal to a temperature over 300°C approximately, introducing vapor of
a crude titanium tetrachloride to contact with said metal, said chloride comprising
a minor amount of metal oxychloride, causing a reaction to convert a substantial part
of the oxychloride to substances which are less volatile than titanium tetrachloride,
removing such substances in condensed state from the titanium tetrachloride in fluid
state, and recovering thus purified titanium tetrachloride.
2. The method as recited in Claim 1, in which said oxychloride comprises TiOCl2.
3. The method as recited in each of Claim 1 or 2, in which said oxychloride comprises
VOC13.
4. The method as recited in Claim 1, in which said catalytic metal substantially consists
of copper.
5. The method as recited in Claim 4, in which said temperature is comprised between
400 and 650°C, approximately.
6. The claim as recited in Claim 1, in which said catalytic metal substantially consists
of iron, with the temperature being over 550°C approximately.
7. The method as recited in Claim 6, in which said temperature is comprised between
600 and 800°C approximately.